2001 Pontiac Aztek is running hot. Do I need to change the thermostat or could the radiator just need flushing? Thermostat has been changed not long ago.

Try reverse flushing the cooling system. If the problem persists, consider replacing the radiator. Mineral (phosphate scale) build-up may be blocking passages in the radiator/heater core. This link may help:

https://www.askmehelpdesk.com/cars-t...tml#post235973

Afterwards, drain and refill with a 50/50 mixture of recommended antifreeze and distilled water.